The present invention relates in general to telecommunication techniques. More particularly, the invention provides a method and system for handover negotiation in wireless networks. Merely by way of example, the invention is described as it applies to base-station or mobile-station initiated handovers, but it should be recognized that the invention has a broader range of applicability.
Techniques for wireless communications have progressed through the years. A wireless network usually includes base stations and mobile stations. For example, a mobile station (MS) refers to a station that is to be used while in motion or during halts at unspecified geographic locations. As an example, the mobile station is a mobile communication device. In another example, the mobile station is a cellular phone. In yet another example, a base station (BS) refers to a set of equipment that can provide connectivity, management, and control for one or more mobile stations. Often, a mobile station communicates with other devices through an air-interface provided by a base station. For example, the air-interface refers to an interface between the base station and the mobile station. Usually, the air-interface can be changes through a process called mobile station handover (HO). During handover, the mobile station, for example, can migrate from an air-interface provided by one base station to another air-interface provided by another base station. The mobile station handover can be initiated by either the mobile station or the base station for various reasons such as mobile-station movement, change in connection quality, and/or change in network configuration.
FIG. 1 shows a simplified conventional wireless network. The network 100 includes base stations 110, 112, and 114, and a mobile station 120. The base stations 110, 112, and 114 each are connected to a wired network 130. For example, the wired network 130 uses internet protocol (IP). The mobile station 120 communicates through an air-interface with the base station 110. The handover of the mobile station 120 can be initiated by the base station 110 or the mobile station 120.
FIGS. 2 and 3 are simplified conventional diagrams for mobile-station handover initiated by base station in wireless network. In the network 100, the base station 110 sends a request message to the mobile station 120 to initiate a handover. The request includes a list of base stations to which the mobile station 120 can be handed over. If the mobile station 120 determines the requested handover to be suitable, the mobile station 120 selects one base station from the list and sends an acknowledgment message back to the base station 110. For example, in the acknowledge message, the mobile station 120 also informs the base station 110 that the base station 112 has been selected. Subsequently, the mobile station 120 is handed over to the base station 112.
FIG. 4 is a simplified conventional diagram for mobile-station handover initiated by mobile station in wireless network. In the network 100, the mobile station 120 sends a request message to the base station 110 to initiate a handover. For example, the response message includes a list of base stations to which the mobile station 120 can be handed over. In response, the base station 110 sends a response message to the mobile station 120. For example, the response message also includes a list of base stations to which the mobile station 120 can be handed over. If the mobile station 120 determines the handover to be suitable, the mobile station 120 selects one base station from the list and sends an acknowledgment message back to the base station 110. For example, in the acknowledgement message, the mobile station 120 also informs the base station 110 that the base station 112 has been selected. Subsequently, the mobile station 120 is handed over to the base station 112.
As shown in FIGS. 2-4, management messages often are exchanged between a mobile station and a base station during a handover process. For example, the management messages include:
1. MOB_BSHO-REQ: This is a request message sent by a base station to a mobile station to initiate a handover.
2. MOB_MSHO-REQ: This is a request message sent by a mobile station to a base station to initiate a handover.
3. MOB_BSHO-RSP: This is a response message sent by a base station to a mobile station to acknowledge receipt of MOB_MSHO-REQ.
4. MOB_HO-IND: This is an acknowledgment message sent by a mobile station to a base station. For example, the acknowledgment message indicates that the mobile station is about to perform a handover, cancel a handover, or reject a handover.
FIGS. 5 and 6 show simplified conventional partial formats for request message and response message for handover respectively. As shown in FIGS. 5 and 6, the request message is called MOB_BSHO-REQ, and the response message is called MOB_BSHO-RSP. For example, the MOB_BSHO-REQ message is sent from the base station 110 to the mobile station 120 for initiating a handover. As another example, the MOB_BSHO-RSP message is sent from the base station 110 to the mobile station 120 to acknowledge receipt of another request message called MOB_MSHO-REQ.
For carrying out a handover successfully, the mobile station and its corresponding base station often have to agree on a handover configuration. For example, the handover configuration includes a list of base stations to which the mobile station can be handed over, and/or an action time. Since a handover usually is initiated by the mobile station or the base station, the initial handover request often is made based on the current information possessed by the initiating entity. The initial request may not satisfy the receiving entity for carrying out the handover. For example, the mobile station is moving, so the information which the base station has used for making a handover request may not reflect the situation when the mobile station receives the handover request. Therefore handover negotiations often are performed.
Hence it is highly desirable to improve techniques for handover negotiations.